MOUNTAIN VIEW, Calif. — Many parts of America, long considered the breadbasket of the world, are now confronting a once unthinkable phenomenon: food rationing. Major retailers in New York, in areas of New England, and on the West Coast are limiting purchases of flour, rice, and cooking oil as demand outstrips supply. There are also anecdotal reports that some consumers are hoarding grain stocks.

At a Costco Warehouse in Mountain View, Calif., yesterday, shoppers grew frustrated and occasionally uttered expletives as they searched in vain for the large sacks of rice they usually buy.

“Where’s the rice?” an engineer from Palo Alto, Calif., Yajun Liu, said. “You should be able to buy something like rice. This is ridiculous.”

The bustling store in the heart of Silicon Valley usually sells four or five varieties of rice to a clientele largely of Asian immigrants, but only about half a pallet of Indian-grown Basmati rice was left in stock. A 20-pound bag was selling for $15.99.